This little OSL shader applies an amplification factor to another shader. The factor can be more than 1, so for example you can create a material that reflects more light than impinges on it!

That may sound physically impossible, but it could be used for example to fake real-world fluorescence effects, like high-visibility vests and the like. These materials reflect visible light which is augmented by the energy of incoming (invisible) ultraviolet light, which is why they can look so bright, without actually being emissive.

A good technique I have found of simulating neon type plastic materials without it being emissive is to overdrive the colours above 1 (don’t go crazy though as you’ll end up with some weird effects)
I used this technique to good effect on my retro-reflective tape material which can be found on blendswap.
In the screenshot below I used a mix of translucent and glass - overdriving the colours on the translucent to give the colour a neon type look (the RGB values for the orange and green material…

Basically, scaling a Closure Color is the same as scaling the color you feed into the closure. No other magic here, and this script is only usefull if we want to scale lots of closures together (as Closure Color can be an array of [Closure*Color])!